OkHttpClient.java

/*
 * Copyright (C) 2012 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okhttp3;

import java.net.MalformedURLException;
import java.net.Proxy;
import java.net.ProxySelector;
import java.net.UnknownHostException;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;
import javax.net.SocketFactory;
import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;
import okhttp3.internal.Internal;
import okhttp3.internal.Util;
import okhttp3.internal.cache.InternalCache;
import okhttp3.internal.connection.RealConnection;
import okhttp3.internal.connection.RouteDatabase;
import okhttp3.internal.connection.StreamAllocation;
import okhttp3.internal.platform.Platform;
import okhttp3.internal.tls.CertificateChainCleaner;
import okhttp3.internal.tls.OkHostnameVerifier;
import okhttp3.internal.ws.RealWebSocket;

/**
 * Factory for {@linkplain Call calls}, which can be used to send HTTP requests and read their
 * responses.
 *
 * <h3>OkHttpClients should be shared</h3>
 *
 * <p>OkHttp performs best when you create a single {@code OkHttpClient} instance and reuse it for
 * all of your HTTP calls. This is because each client holds its own connection pool and thread
 * pools. Reusing connections and threads reduces latency and saves memory. Conversely, creating a
 * client for each request wastes resources on idle pools.
 *
 * <p>Use {@code new OkHttpClient()} to create a shared instance with the default settings:
 * <pre>   {@code
 *
 *   // The singleton HTTP client.
 *   public final OkHttpClient client = new OkHttpClient();
 * }</pre>
 *
 * <p>Or use {@code new OkHttpClient.Builder()} to create a shared instance with custom settings:
 * <pre>   {@code
 *
 *   // The singleton HTTP client.
 *   public final OkHttpClient client = new OkHttpClient.Builder()
 *       .addInterceptor(new HttpLoggingInterceptor())
 *       .cache(new Cache(cacheDir, cacheSize))
 *       .build();
 * }</pre>
 *
 * <h3>Customize your client with newBuilder()</h3>
 *
 * <p>You can customize a shared OkHttpClient instance with {@link #newBuilder()}. This builds a
 * client that shares the same connection pool, thread pools, and configuration. Use the builder
 * methods to configure the derived client for a specific purpose.
 *
 * <p>This example shows a call with a short 500 millisecond timeout: <pre>   {@code
 *
 *   OkHttpClient eagerClient = client.newBuilder()
 *       .readTimeout(500, TimeUnit.MILLISECONDS)
 *       .build();
 *   Response response = eagerClient.newCall(request).execute();
 * }</pre>
 *
 * <h3>Shutdown isn't necessary</h3>
 *
 * <p>The threads and connections that are held will be released automatically if they remain idle.
 * But if you are writing a application that needs to aggressively release unused resources you may
 * do so.
 *
 * <p>Shutdown the dispatcher's executor service with {@link ExecutorService#shutdown shutdown()}.
 * This will also cause future calls to the client to be rejected. <pre>   {@code
 *
 *     client.dispatcher().executorService().shutdown();
 * }</pre>
 *
 * <p>Clear the connection pool with {@link ConnectionPool#evictAll() evictAll()}. Note that the
 * connection pool's daemon thread may not exit immediately. <pre>   {@code
 *
 *     client.connectionPool().evictAll();
 * }</pre>
 *
 * <p>If your client has a cache, call {@link Cache#close close()}. Note that it is an error to
 * create calls against a cache that is closed, and doing so will cause the call to crash.
 * <pre>   {@code
 *
 *     client.cache().close();
 * }</pre>
 *
 * <p>OkHttp also uses daemon threads for HTTP/2 connections. These will exit automatically if they
 * remain idle.
 */
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
  static final List<Protocol> DEFAULT_PROTOCOLS = Util.immutableList(
      Protocol.HTTP_2, Protocol.HTTP_1_1);

  static final List<ConnectionSpec> DEFAULT_CONNECTION_SPECS = Util.immutableList(
      ConnectionSpec.MODERN_TLS, ConnectionSpec.COMPATIBLE_TLS, ConnectionSpec.CLEARTEXT);

  static {
    Internal.instance = new Internal() {
      @Override public void addLenient(Headers.Builder builder, String line) {
        builder.addLenient(line);
      }

      @Override public void addLenient(Headers.Builder builder, String name, String value) {
        builder.addLenient(name, value);
      }

      @Override public void setCache(OkHttpClient.Builder builder, InternalCache internalCache) {
        builder.setInternalCache(internalCache);
      }

      @Override public boolean connectionBecameIdle(
          ConnectionPool pool, RealConnection connection) {
        return pool.connectionBecameIdle(connection);
      }

      @Override public RealConnection get(
          ConnectionPool pool, Address address, StreamAllocation streamAllocation) {
        return pool.get(address, streamAllocation);
      }

      @Override public void put(ConnectionPool pool, RealConnection connection) {
        pool.put(connection);
      }

      @Override public RouteDatabase routeDatabase(ConnectionPool connectionPool) {
        return connectionPool.routeDatabase;
      }

      @Override
      public void apply(ConnectionSpec tlsConfiguration, SSLSocket sslSocket, boolean isFallback) {
        tlsConfiguration.apply(sslSocket, isFallback);
      }

      @Override public HttpUrl getHttpUrlChecked(String url)
          throws MalformedURLException, UnknownHostException {
        return HttpUrl.getChecked(url);
      }

      @Override public StreamAllocation streamAllocation(Call call) {
        return ((RealCall) call).streamAllocation();
      }

      @Override public Call newWebSocketCall(OkHttpClient client, Request originalRequest) {
        return new RealCall(client, originalRequest, true);
      }
    };
  }

  final Dispatcher dispatcher;
  final Proxy proxy;
  final List<Protocol> protocols;
  final List<ConnectionSpec> connectionSpecs;
  final List<Interceptor> interceptors;
  final List<Interceptor> networkInterceptors;
  final ProxySelector proxySelector;
  final CookieJar cookieJar;
  final Cache cache;
  final InternalCache internalCache;
  final SocketFactory socketFactory;
  final SSLSocketFactory sslSocketFactory;
  final CertificateChainCleaner certificateChainCleaner;
  final HostnameVerifier hostnameVerifier;
  final CertificatePinner certificatePinner;
  final Authenticator proxyAuthenticator;
  final Authenticator authenticator;
  final ConnectionPool connectionPool;
  final Dns dns;
  final boolean followSslRedirects;
  final boolean followRedirects;
  final boolean retryOnConnectionFailure;
  final int connectTimeout;
  final int readTimeout;
  final int writeTimeout;
  final int pingInterval;

  public OkHttpClient() {
    this(new Builder());
  }

  OkHttpClient(Builder builder) {
    this.dispatcher = builder.dispatcher;
    this.proxy = builder.proxy;
    this.protocols = builder.protocols;
    this.connectionSpecs = builder.connectionSpecs;
    this.interceptors = Util.immutableList(builder.interceptors);
    this.networkInterceptors = Util.immutableList(builder.networkInterceptors);
    this.proxySelector = builder.proxySelector;
    this.cookieJar = builder.cookieJar;
    this.cache = builder.cache;
    this.internalCache = builder.internalCache;
    this.socketFactory = builder.socketFactory;

    boolean isTLS = false;
    for (ConnectionSpec spec : connectionSpecs) {
      isTLS = isTLS || spec.isTls();
    }

    if (builder.sslSocketFactory != null || !isTLS) {
      this.sslSocketFactory = builder.sslSocketFactory;
      this.certificateChainCleaner = builder.certificateChainCleaner;
    } else {
      X509TrustManager trustManager = systemDefaultTrustManager();
      this.sslSocketFactory = systemDefaultSslSocketFactory(trustManager);
      this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
    }

    this.hostnameVerifier = builder.hostnameVerifier;
    this.certificatePinner = builder.certificatePinner.withCertificateChainCleaner(
        certificateChainCleaner);
    this.proxyAuthenticator = builder.proxyAuthenticator;
    this.authenticator = builder.authenticator;
    this.connectionPool = builder.connectionPool;
    this.dns = builder.dns;
    this.followSslRedirects = builder.followSslRedirects;
    this.followRedirects = builder.followRedirects;
    this.retryOnConnectionFailure = builder.retryOnConnectionFailure;
    this.connectTimeout = builder.connectTimeout;
    this.readTimeout = builder.readTimeout;
    this.writeTimeout = builder.writeTimeout;
    this.pingInterval = builder.pingInterval;
  }

  private X509TrustManager systemDefaultTrustManager() {
    try {
      TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
          TrustManagerFactory.getDefaultAlgorithm());
      trustManagerFactory.init((KeyStore) null);
      TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
      if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
        throw new IllegalStateException("Unexpected default trust managers:"
            + Arrays.toString(trustManagers));
      }
      return (X509TrustManager) trustManagers[0];
    } catch (GeneralSecurityException e) {
      throw new AssertionError(); // The system has no TLS. Just give up.
    }
  }

  private SSLSocketFactory systemDefaultSslSocketFactory(X509TrustManager trustManager) {
    try {
      SSLContext sslContext = SSLContext.getInstance("TLS");
      sslContext.init(null, new TrustManager[] { trustManager }, null);
      return sslContext.getSocketFactory();
    } catch (GeneralSecurityException e) {
      throw new AssertionError(); // The system has no TLS. Just give up.
    }
  }

  /** Default connect timeout (in milliseconds). */
  public int connectTimeoutMillis() {
    return connectTimeout;
  }

  /** Default read timeout (in milliseconds). */
  public int readTimeoutMillis() {
    return readTimeout;
  }

  /** Default write timeout (in milliseconds). */
  public int writeTimeoutMillis() {
    return writeTimeout;
  }

  /** Web socket ping interval (in milliseconds). */
  public int pingIntervalMillis() {
    return pingInterval;
  }

  public Proxy proxy() {
    return proxy;
  }

  public ProxySelector proxySelector() {
    return proxySelector;
  }

  public CookieJar cookieJar() {
    return cookieJar;
  }

  public Cache cache() {
    return cache;
  }

  InternalCache internalCache() {
    return cache != null ? cache.internalCache : internalCache;
  }

  public Dns dns() {
    return dns;
  }

  public SocketFactory socketFactory() {
    return socketFactory;
  }

  public SSLSocketFactory sslSocketFactory() {
    return sslSocketFactory;
  }

  public HostnameVerifier hostnameVerifier() {
    return hostnameVerifier;
  }

  public CertificatePinner certificatePinner() {
    return certificatePinner;
  }

  public Authenticator authenticator() {
    return authenticator;
  }

  public Authenticator proxyAuthenticator() {
    return proxyAuthenticator;
  }

  public ConnectionPool connectionPool() {
    return connectionPool;
  }

  public boolean followSslRedirects() {
    return followSslRedirects;
  }

  public boolean followRedirects() {
    return followRedirects;
  }

  public boolean retryOnConnectionFailure() {
    return retryOnConnectionFailure;
  }

  public Dispatcher dispatcher() {
    return dispatcher;
  }

  public List<Protocol> protocols() {
    return protocols;
  }

  public List<ConnectionSpec> connectionSpecs() {
    return connectionSpecs;
  }

  /**
   * Returns an immutable list of interceptors that observe the full span of each call: from before
   * the connection is established (if any) until after the response source is selected (either the
   * origin server, cache, or both).
   */
  public List<Interceptor> interceptors() {
    return interceptors;
  }

  /**
   * Returns an immutable list of interceptors that observe a single network request and response.
   * These interceptors must call {@link Interceptor.Chain#proceed} exactly once: it is an error for
   * a network interceptor to short-circuit or repeat a network request.
   */
  public List<Interceptor> networkInterceptors() {
    return networkInterceptors;
  }

  /**
   * Prepares the {@code request} to be executed at some point in the future.
   */
  @Override public Call newCall(Request request) {
    return new RealCall(this, request, false /* for web socket */);
  }

  /**
   * Uses {@code request} to connect a new web socket.
   */
  @Override public WebSocket newWebSocket(Request request, WebSocketListener listener) {
    RealWebSocket webSocket = new RealWebSocket(request, listener, new SecureRandom());
    webSocket.connect(this);
    return webSocket;
  }

  public Builder newBuilder() {
    return new Builder(this);
  }

  public static final class Builder {
    Dispatcher dispatcher;
    Proxy proxy;
    List<Protocol> protocols;
    List<ConnectionSpec> connectionSpecs;
    final List<Interceptor> interceptors = new ArrayList<>();
    final List<Interceptor> networkInterceptors = new ArrayList<>();
    ProxySelector proxySelector;
    CookieJar cookieJar;
    Cache cache;
    InternalCache internalCache;
    SocketFactory socketFactory;
    SSLSocketFactory sslSocketFactory;
    CertificateChainCleaner certificateChainCleaner;
    HostnameVerifier hostnameVerifier;
    CertificatePinner certificatePinner;
    Authenticator proxyAuthenticator;
    Authenticator authenticator;
    ConnectionPool connectionPool;
    Dns dns;
    boolean followSslRedirects;
    boolean followRedirects;
    boolean retryOnConnectionFailure;
    int connectTimeout;
    int readTimeout;
    int writeTimeout;
    int pingInterval;

    public Builder() {
      dispatcher = new Dispatcher();
      protocols = DEFAULT_PROTOCOLS;
      connectionSpecs = DEFAULT_CONNECTION_SPECS;
      proxySelector = ProxySelector.getDefault();
      cookieJar = CookieJar.NO_COOKIES;
      socketFactory = SocketFactory.getDefault();
      hostnameVerifier = OkHostnameVerifier.INSTANCE;
      certificatePinner = CertificatePinner.DEFAULT;
      proxyAuthenticator = Authenticator.NONE;
      authenticator = Authenticator.NONE;
      connectionPool = new ConnectionPool();
      dns = Dns.SYSTEM;
      followSslRedirects = true;
      followRedirects = true;
      retryOnConnectionFailure = true;
      connectTimeout = 10_000;
      readTimeout = 10_000;
      writeTimeout = 10_000;
      pingInterval = 0;
    }

    Builder(OkHttpClient okHttpClient) {
      this.dispatcher = okHttpClient.dispatcher;
      this.proxy = okHttpClient.proxy;
      this.protocols = okHttpClient.protocols;
      this.connectionSpecs = okHttpClient.connectionSpecs;
      this.interceptors.addAll(okHttpClient.interceptors);
      this.networkInterceptors.addAll(okHttpClient.networkInterceptors);
      this.proxySelector = okHttpClient.proxySelector;
      this.cookieJar = okHttpClient.cookieJar;
      this.internalCache = okHttpClient.internalCache;
      this.cache = okHttpClient.cache;
      this.socketFactory = okHttpClient.socketFactory;
      this.sslSocketFactory = okHttpClient.sslSocketFactory;
      this.certificateChainCleaner = okHttpClient.certificateChainCleaner;
      this.hostnameVerifier = okHttpClient.hostnameVerifier;
      this.certificatePinner = okHttpClient.certificatePinner;
      this.proxyAuthenticator = okHttpClient.proxyAuthenticator;
      this.authenticator = okHttpClient.authenticator;
      this.connectionPool = okHttpClient.connectionPool;
      this.dns = okHttpClient.dns;
      this.followSslRedirects = okHttpClient.followSslRedirects;
      this.followRedirects = okHttpClient.followRedirects;
      this.retryOnConnectionFailure = okHttpClient.retryOnConnectionFailure;
      this.connectTimeout = okHttpClient.connectTimeout;
      this.readTimeout = okHttpClient.readTimeout;
      this.writeTimeout = okHttpClient.writeTimeout;
      this.pingInterval = okHttpClient.pingInterval;
    }

    /**
     * Sets the default connect timeout for new connections. A value of 0 means no timeout,
     * otherwise values must be between 1 and {@link Integer#MAX_VALUE} when converted to
     * milliseconds.
     */
    public Builder connectTimeout(long timeout, TimeUnit unit) {
      connectTimeout = checkDuration("timeout", timeout, unit);
      return this;
    }

    /**
     * Sets the default read timeout for new connections. A value of 0 means no timeout, otherwise
     * values must be between 1 and {@link Integer#MAX_VALUE} when converted to milliseconds.
     */
    public Builder readTimeout(long timeout, TimeUnit unit) {
      readTimeout = checkDuration("timeout", timeout, unit);
      return this;
    }

    /**
     * Sets the default write timeout for new connections. A value of 0 means no timeout, otherwise
     * values must be between 1 and {@link Integer#MAX_VALUE} when converted to milliseconds.
     */
    public Builder writeTimeout(long timeout, TimeUnit unit) {
      writeTimeout = checkDuration("timeout", timeout, unit);
      return this;
    }

    /**
     * Sets the interval between web socket pings initiated by this client. Use this to
     * automatically send web socket ping frames until either the web socket fails or it is closed.
     * This keeps the connection alive and may detect connectivity failures early. No timeouts are
     * enforced on the acknowledging pongs.
     *
     * <p>The default value of 0 disables client-initiated pings.
     */
    public Builder pingInterval(long interval, TimeUnit unit) {
      pingInterval = checkDuration("interval", interval, unit);
      return this;
    }

    private static int checkDuration(String name, long duration, TimeUnit unit) {
      if (duration < 0) throw new IllegalArgumentException(name + " < 0");
      if (unit == null) throw new NullPointerException("unit == null");
      long millis = unit.toMillis(duration);
      if (millis > Integer.MAX_VALUE) throw new IllegalArgumentException(name + " too large.");
      if (millis == 0 && duration > 0) throw new IllegalArgumentException(name + " too small.");
      return (int) millis;
    }

    /**
     * Sets the HTTP proxy that will be used by connections created by this client. This takes
     * precedence over {@link #proxySelector}, which is only honored when this proxy is null (which
     * it is by default). To disable proxy use completely, call {@code setProxy(Proxy.NO_PROXY)}.
     */
    public Builder proxy(Proxy proxy) {
      this.proxy = proxy;
      return this;
    }

    /**
     * Sets the proxy selection policy to be used if no {@link #proxy proxy} is specified
     * explicitly. The proxy selector may return multiple proxies; in that case they will be tried
     * in sequence until a successful connection is established.
     *
     * <p>If unset, the {@link ProxySelector#getDefault() system-wide default} proxy selector will
     * be used.
     */
    public Builder proxySelector(ProxySelector proxySelector) {
      this.proxySelector = proxySelector;
      return this;
    }

    /**
     * Sets the handler that can accept cookies from incoming HTTP responses and provides cookies to
     * outgoing HTTP requests.
     *
     * <p>If unset, {@linkplain CookieJar#NO_COOKIES no cookies} will be accepted nor provided.
     */
    public Builder cookieJar(CookieJar cookieJar) {
      if (cookieJar == null) throw new NullPointerException("cookieJar == null");
      this.cookieJar = cookieJar;
      return this;
    }

    /** Sets the response cache to be used to read and write cached responses. */
    void setInternalCache(InternalCache internalCache) {
      this.internalCache = internalCache;
      this.cache = null;
    }

    /** Sets the response cache to be used to read and write cached responses. */
    public Builder cache(Cache cache) {
      this.cache = cache;
      this.internalCache = null;
      return this;
    }

    /**
     * Sets the DNS service used to lookup IP addresses for hostnames.
     *
     * <p>If unset, the {@link Dns#SYSTEM system-wide default} DNS will be used.
     */
    public Builder dns(Dns dns) {
      if (dns == null) throw new NullPointerException("dns == null");
      this.dns = dns;
      return this;
    }

    /**
     * Sets the socket factory used to create connections. OkHttp only uses the parameterless {@link
     * SocketFactory#createSocket() createSocket()} method to create unconnected sockets. Overriding
     * this method, e. g., allows the socket to be bound to a specific local address.
     *
     * <p>If unset, the {@link SocketFactory#getDefault() system-wide default} socket factory will
     * be used.
     */
    public Builder socketFactory(SocketFactory socketFactory) {
      if (socketFactory == null) throw new NullPointerException("socketFactory == null");
      this.socketFactory = socketFactory;
      return this;
    }

    /**
     * Sets the socket factory used to secure HTTPS connections. If unset, the system default will
     * be used.
     *
     * @deprecated {@code SSLSocketFactory} does not expose its {@link X509TrustManager}, which is
     *     a field that OkHttp needs to build a clean certificate chain. This method instead must
     *     use reflection to extract the trust manager. Applications should prefer to call {@link
     *     #sslSocketFactory(SSLSocketFactory, X509TrustManager)}, which avoids such reflection.
     */
    public Builder sslSocketFactory(SSLSocketFactory sslSocketFactory) {
      if (sslSocketFactory == null) throw new NullPointerException("sslSocketFactory == null");
      X509TrustManager trustManager = Platform.get().trustManager(sslSocketFactory);
      if (trustManager == null) {
        throw new IllegalStateException("Unable to extract the trust manager on " + Platform.get()
            + ", sslSocketFactory is " + sslSocketFactory.getClass());
      }
      this.sslSocketFactory = sslSocketFactory;
      this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
      return this;
    }

    /**
     * Sets the socket factory and trust manager used to secure HTTPS connections. If unset, the
     * system defaults will be used.
     *
     * <p>Most applications should not call this method, and instead use the system defaults. Those
     * classes include special optimizations that can be lost if the implementations are decorated.
     *
     * <p>If necessary, you can create and configure the defaults yourself with the following code:
     *
     * <pre>   {@code
     *
     *   TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
     *       TrustManagerFactory.getDefaultAlgorithm());
     *   trustManagerFactory.init((KeyStore) null);
     *   TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
     *   if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
     *     throw new IllegalStateException("Unexpected default trust managers:"
     *         + Arrays.toString(trustManagers));
     *   }
     *   X509TrustManager trustManager = (X509TrustManager) trustManagers[0];
     *
     *   SSLContext sslContext = SSLContext.getInstance("TLS");
     *   sslContext.init(null, new TrustManager[] { trustManager }, null);
     *   SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
     *
     *   OkHttpClient client = new OkHttpClient.Builder()
     *       .sslSocketFactory(sslSocketFactory, trustManager);
     *       .build();
     * }</pre>
     */
    public Builder sslSocketFactory(
        SSLSocketFactory sslSocketFactory, X509TrustManager trustManager) {
      if (sslSocketFactory == null) throw new NullPointerException("sslSocketFactory == null");
      if (trustManager == null) throw new NullPointerException("trustManager == null");
      this.sslSocketFactory = sslSocketFactory;
      this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
      return this;
    }

    /**
     * Sets the verifier used to confirm that response certificates apply to requested hostnames for
     * HTTPS connections.
     *
     * <p>If unset, a default hostname verifier will be used.
     */
    public Builder hostnameVerifier(HostnameVerifier hostnameVerifier) {
      if (hostnameVerifier == null) throw new NullPointerException("hostnameVerifier == null");
      this.hostnameVerifier = hostnameVerifier;
      return this;
    }

    /**
     * Sets the certificate pinner that constrains which certificates are trusted. By default HTTPS
     * connections rely on only the {@link #sslSocketFactory SSL socket factory} to establish trust.
     * Pinning certificates avoids the need to trust certificate authorities.
     */
    public Builder certificatePinner(CertificatePinner certificatePinner) {
      if (certificatePinner == null) throw new NullPointerException("certificatePinner == null");
      this.certificatePinner = certificatePinner;
      return this;
    }

    /**
     * Sets the authenticator used to respond to challenges from origin servers. Use {@link
     * #proxyAuthenticator} to set the authenticator for proxy servers.
     *
     * <p>If unset, the {@linkplain Authenticator#NONE no authentication will be attempted}.
     */
    public Builder authenticator(Authenticator authenticator) {
      if (authenticator == null) throw new NullPointerException("authenticator == null");
      this.authenticator = authenticator;
      return this;
    }

    /**
     * Sets the authenticator used to respond to challenges from proxy servers. Use {@link
     * #authenticator} to set the authenticator for origin servers.
     *
     * <p>If unset, the {@linkplain Authenticator#NONE no authentication will be attempted}.
     */
    public Builder proxyAuthenticator(Authenticator proxyAuthenticator) {
      if (proxyAuthenticator == null) throw new NullPointerException("proxyAuthenticator == null");
      this.proxyAuthenticator = proxyAuthenticator;
      return this;
    }

    /**
     * Sets the connection pool used to recycle HTTP and HTTPS connections.
     *
     * <p>If unset, a new connection pool will be used.
     */
    public Builder connectionPool(ConnectionPool connectionPool) {
      if (connectionPool == null) throw new NullPointerException("connectionPool == null");
      this.connectionPool = connectionPool;
      return this;
    }

    /**
     * Configure this client to follow redirects from HTTPS to HTTP and from HTTP to HTTPS.
     *
     * <p>If unset, protocol redirects will be followed. This is different than the built-in {@code
     * HttpURLConnection}'s default.
     */
    public Builder followSslRedirects(boolean followProtocolRedirects) {
      this.followSslRedirects = followProtocolRedirects;
      return this;
    }

    /** Configure this client to follow redirects. If unset, redirects will be followed. */
    public Builder followRedirects(boolean followRedirects) {
      this.followRedirects = followRedirects;
      return this;
    }

    /**
     * Configure this client to retry or not when a connectivity problem is encountered. By default,
     * this client silently recovers from the following problems:
     *
     * <ul>
     *   <li><strong>Unreachable IP addresses.</strong> If the URL's host has multiple IP addresses,
     *       failure to reach any individual IP address doesn't fail the overall request. This can
     *       increase availability of multi-homed services.
     *   <li><strong>Stale pooled connections.</strong> The {@link ConnectionPool} reuses sockets
     *       to decrease request latency, but these connections will occasionally time out.
     *   <li><strong>Unreachable proxy servers.</strong> A {@link ProxySelector} can be used to
     *       attempt multiple proxy servers in sequence, eventually falling back to a direct
     *       connection.
     * </ul>
     *
     * Set this to false to avoid retrying requests when doing so is destructive. In this case the
     * calling application should do its own recovery of connectivity failures.
     */
    public Builder retryOnConnectionFailure(boolean retryOnConnectionFailure) {
      this.retryOnConnectionFailure = retryOnConnectionFailure;
      return this;
    }

    /**
     * Sets the dispatcher used to set policy and execute asynchronous requests. Must not be null.
     */
    public Builder dispatcher(Dispatcher dispatcher) {
      if (dispatcher == null) throw new IllegalArgumentException("dispatcher == null");
      this.dispatcher = dispatcher;
      return this;
    }

    /**
     * Configure the protocols used by this client to communicate with remote servers. By default
     * this client will prefer the most efficient transport available, falling back to more
     * ubiquitous protocols. Applications should only call this method to avoid specific
     * compatibility problems, such as web servers that behave incorrectly when HTTP/2 is enabled.
     *
     * <p>The following protocols are currently supported:
     *
     * <ul>
     *     <li><a href="http://www.w3.org/Protocols/rfc2616/rfc2616.html">http/1.1</a>
     *     <li><a href="http://tools.ietf.org/html/draft-ietf-httpbis-http2-17">h2</a>
     * </ul>
     *
     * <p><strong>This is an evolving set.</strong> Future releases include support for transitional
     * protocols. The http/1.1 transport will never be dropped.
     *
     * <p>If multiple protocols are specified, <a
     * href="http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg">ALPN</a> will be used to
     * negotiate a transport.
     *
     * <p>{@link Protocol#HTTP_1_0} is not supported in this set. Requests are initiated with {@code
     * HTTP/1.1} only. If the server responds with {@code HTTP/1.0}, that will be exposed by {@link
     * Response#protocol()}.
     *
     * @param protocols the protocols to use, in order of preference. The list must contain {@link
     * Protocol#HTTP_1_1}. It must not contain null or {@link Protocol#HTTP_1_0}.
     */
    public Builder protocols(List<Protocol> protocols) {
      // Create a private copy of the list.
      protocols = new ArrayList<>(protocols);

      // Validate that the list has everything we require and nothing we forbid.
      if (!protocols.contains(Protocol.HTTP_1_1)) {
        throw new IllegalArgumentException("protocols doesn't contain http/1.1: " + protocols);
      }
      if (protocols.contains(Protocol.HTTP_1_0)) {
        throw new IllegalArgumentException("protocols must not contain http/1.0: " + protocols);
      }
      if (protocols.contains(null)) {
        throw new IllegalArgumentException("protocols must not contain null");
      }

      // Remove protocols that we no longer support.
      if (protocols.contains(Protocol.SPDY_3)) {
        protocols.remove(Protocol.SPDY_3);
      }

      // Assign as an unmodifiable list. This is effectively immutable.
      this.protocols = Collections.unmodifiableList(protocols);
      return this;
    }

    public Builder connectionSpecs(List<ConnectionSpec> connectionSpecs) {
      this.connectionSpecs = Util.immutableList(connectionSpecs);
      return this;
    }

    /**
     * Returns a modifiable list of interceptors that observe the full span of each call: from
     * before the connection is established (if any) until after the response source is selected
     * (either the origin server, cache, or both).
     */
    public List<Interceptor> interceptors() {
      return interceptors;
    }

    public Builder addInterceptor(Interceptor interceptor) {
      interceptors.add(interceptor);
      return this;
    }

    /**
     * Returns a modifiable list of interceptors that observe a single network request and response.
     * These interceptors must call {@link Interceptor.Chain#proceed} exactly once: it is an error
     * for a network interceptor to short-circuit or repeat a network request.
     */
    public List<Interceptor> networkInterceptors() {
      return networkInterceptors;
    }

    public Builder addNetworkInterceptor(Interceptor interceptor) {
      networkInterceptors.add(interceptor);
      return this;
    }

    public OkHttpClient build() {
      return new OkHttpClient(this);
    }
  }
}